This invention relates to autonomous private cellular systems operating in public cellular system frequency bands and, more particularly, to a system and method for manually searching for autonomous private systems.
A wireless communication system, in the form of a cellular system, is designed to cover a large geographic area. The system is divided into numerous cells providing air interface between mobile stations and land-based systems. Each cell includes a base station for communicating with mobile stations. These wireless communication systems maintain a set of frequencies that are used for traffic channels and control channels. Frequency planning is necessary in order to determine which of the frequencies should be used at any given time.
Recently, cellular-based system design is used as a foundation for smaller systems, such as private cellular or wireless office systems. These private cellular systems may share the frequency spectrum with the public cellular systems. The private cellular system user must be defined as a normal cellular subscriber in the subscriber database of the public cellular system, and the user""s mobile station must be defined in both the private cellular system and the public cellular system. These are preconditions to enable the mobile station to roam between the public and private cellular system and to perform authentication. It will also be required for the mobile station to find the private cellular system. Use of neighbor cell pointers from the public system to the private system is not desirable, since it will increase the administration of the public system. Instead, a mechanism based on stored information in the terminal is preferred. Such a mechanism is defined in ANSI-136.
A frequency re-plan is usually performed to give more capacity or to improve coverage. Since the public cellular systems have a limited spectrum based on the licensed frequency band, capacity is increased by increasing the number of frequencies in each cell site and/or installing more cell sites. Both methods bring new frequencies in use in the area affected. Since frequencies are re-used, other cell sites frequency use is also affected and they may have to re-tune their transceivers to other frequencies to accommodate the first change. This produces a rippling effect. The private cellular systems monitor the public cellular system and avoid frequencies used nearby in the public cellular systems. A change in the public cellular system""s frequency use thus changes the frequency use of the private cellular systems.
A mobile station will not automatically find an autonomous private cellular system if a frequency re-plan of the control frequency has taken place in either the private or public cellular systems. Also, the first time a mobile station wants to acquire service from a private cellular system, the appropriate parameters, such as the public service profile/private operating frequency (PSP/POF) parameters in the ANSI 136, Rev. A standard are not defined in the mobile station and it will not automatically find the private cellular system.
If the mobile station cannot automatically find the private cellular system, due to, e.g., the stored PSP/POF information is not correct due to a frequency re-plan, then a manual search must be invoked. Presently, the ANSI-136 Rev. A standard outlines a manual search procedure to find a private cellular system. However, the search is limited to the frequency band the mobile station is presently camping on. As a result, autonomous private cellular systems operating on other bands cannot be found. In a publication entitled xe2x80x9cGlobal Operators Forum Implementation Guide: Non-Public Mode Operation in TIA/EIA-136-A Compliant Mobile Stationsxe2x80x9d, Version 4, December 1998, a modified manual search is proposed. In this proposal, the mobile station searches all bands if the private system is not found in the frequency band the mobile station was last camping on. Searching all bands can take more than fifteen minutes, resulting in substantial inconvenience for the end user. A mobile station designed according to ANSI-136 Rev. A can also be configured to find a private cellular system during a power-up scan. However, doing so limits the usage of the intelligent roaming database (IRDB) for public cellular system and provides undesirable behavior, such as long scanning times whenever a power-on is performed in the public cellular system and limited roaming capabilities.
The present invention is directed to solving one or more of the problems discussed above in a novel and simple manner.
In accordance with the invention there is provided a unique and more robust manually initiated search procedure for private cellular systems in a mobile station, independent of the frequency band the mobile station was last camping on.
Broadly, there is disclosed herein in a mobile station for use in both public cellular systems and private cellular systems, the private cellular system using select allocated frequency bands from the public cellular systems, a system for manually searching for one of the private cellular systems. The system comprises a memory storing information on select frequency bands. A transmitter and receiver is provided for communicating in the public cellular systems and the private cellular systems. An input initiates a manual search for one of the private cellular systems using the stored information on one of the select frequency bands. A programmed processor is operatively coupled to the memory, the transmitter and receiver and the input for operating the transmitter and receiver to search for the one private cellular system using the one of the select frequency bands.
It is a feature of the invention that the memory stores a directory of the private cellular systems including identification information and a frequency band for each private cellular system. The input selects from the directory of private systems and the programmed processor operates the transmitter and receiver to search for the one of the private cellular systems on the stored frequency band for the selected private cellular system. It is another feature of the invention that the input can be used to update the directory.
It is another feature of the invention that the memory stores plural predefined frequency bands. The input selects from the plural predefined frequency bands and the programmed processor operates the transmitter and receiver to search for the one of the private cellular systems on the selected predefined frequency band for one of the private cellular systems.
It is another feature of the invention that the programmed processor is operated to initially search using strongest control channels found in the selected predefined frequency band.
There is disclosed in accordance with another aspect of the invention the method of operating a mobile station used in both public cellular systems and private cellular systems, the private cellular systems using select allocated frequency bands from the public cellular systems, for manually searching for a private cellular system. The method comprises the steps of storing information on select frequency bands; initiating a manual search for one of the private cellular systems using the stored information on one of the select frequency bands; and operating a transmitter and receiver communicating in the public cellular systems and the private cellular systems to search for the one private cellular system using the one of the select frequency bands.
Further features and advantages of the invention will be readily apparent from the specification and from the drawings.